The invention relates to a sieve frame for plansifters, the sieve frame having a sieve covering, a bottom, and a sieve cleaner for the sieve frame. Such sieve cleaners are inserted in the sieve frame of the plansifter so that they will move below the sieve covering in response the shaking movement of the sieve and, in doing so, bring their cleaning devices into contact with the sieve covering in order to clean the latter.
With conventional sieve cleaners, the cleaning devices are not constantly in contact with the sieve covering, but the cleaning effect is created essentially by the cleaning devices hitting against the sieve covering. This is facilitated, for example, by the fact that the sieve cleaner rests with one foot on an ondular grid arranged in parallel to the sieve cleaner, which is set vibrating as it moves across the ondular grid.
A conventional sieve frame has a sieve cleaner tiltingly supported with its foot on the bottom of the frame such that, at any given time, only a part of the cleaning brushes engage the sieve covering. Another sieve cleaner is known which has the form of a three-armed star whose cleaning devices are arranged in the area of the free ends of the three cantilever arms arranged in an angular distance of some 120 degrees. This sieve cleaner rests on the level sieve bottom with one foot so that, with the shaking motion of the sieve, the sieve cleaner executes a wobbling movement and hits the sieve covering. The foot can engage in a bottom-clearing device that supports the clearing of the sieve-throughs toward a slot opening provided at the edge of the sieve frame.
The advantage of this known sieve cleaner is that it allows a small overall height of the sieve frame, and that it can easily reach into the corners of the sieve frame with its cantilever arms so that the sieve covering is thoroughly cleaned, including in the corner zones.
When the sieve cleaner bumps against the edge of the sieve frame, the free ends of two arms are in contact with the edge of the sieve frame while the third arm points to the center of the sieve. This results in the fact that cleaning devices treat the central area of the sieve statistically more often than the peripheral areas. This can cause an uneven cleaning effect and lead to an increased wear of the sieve covering in the center of the sieve.
The problem to be solved by the invention is to provide a sieve frame and a sieve cleaner that allow an intensive as well as gentle cleaning of the sieve covering.
This problem is solved by a sieve frame comprising a sieve covering, a bottom, and at least one sieve cleaner having a foot and a plurality of cleaning heads having, for example, a brush-like or nubby configuration. The heads are configured to move erratically on the bottom in response to a shaking or vibrating movement of the sieve frame. One of the foot and at least part of the foot closest to the cleaning heads resiliently supports the sieve cleaner, for example by a spring, such that the cleaning heads are under a elastic initial tension against the sieve covering. The problem further is solved by a sieve cleaner for use with the sieve frame, the foot of the sieve cleaner being arranged so as to be offset with respect to the cleaning heads. The part of the foot closest to the cleaning heads is located between the cleaning heads and the center of gravity of the sieve cleaner.
Various advantageous embodiments of the invention can be taken from the appended claims.
With the sieve frame in accordance with the invention the cleaning devices are resiliently prestressed against the sieve covering by a foot supported by a spring so that potential dimensional tolerances in the distance between the sieve bottom and the sieve covering, e.g. owing to a slight arching of the sieve bottom, do not cause the sieve cleaner to get jammed.
The cleaning effect is not provided by hitting against the sieve covering, but instead by the fact that the cleaning devices are running over the sieve covering. The fact that all cleaning devices are continually and efficiently cleaning the sieve more than compensates for forgoing the hits against the sieve covering. Another advantage results from more evenly distributed contact of the cleaning devices with the bottom, thus resulting in less wear and tear in one particular area.
According to another aspect of the invention, in an embodiment of the sieve cleaner, the bulk of the cleaning devices is essentially arranged in a line, and a spacer that is not, or at least less densely, fitted with cleaning devices protrudes from the line of cleaning devices toward one side.
When the sieve cleaner bumps against the edge of the sieve frame, it can be aligned in such a manner that the line of cleaning devices is almost in parallel with the edge of the sieve frame. This assists in a relatively large surface of the sieve covering being treated by the cleaning devices in the area close to the edges, while the spacerxe2x80x94protruding to the inside at this momentxe2x80x94is less or not at all involved in the cleaning. In this way, on the statistical average, a more even cleaning of the sieve covering is achieved and an excessive wear of the sieve covering in the central area of the sieve is avoided.
Preferably, the spacer is not fitted with cleaning devices and is arranged in a T-shape in reference to the line of cleaning devices. Also preferably, the foot on which the sieve cleaner rests on the level sieve bottom, which can simultaneously serve as a bottom-clearing-device, is provided under the spacer so that it is in contact with the sieve bottom in at least two places. This serves the purpose of limiting the possible movement of the sieve cleaner so that the entire line of the cleaning devices is permanently kept in contact with the sieve covering.
The sieve frames of a plansifter usually are of a square layout. It is possible to obtain a specifically even cleaning effect when the length of the sieve cleaner measured from the line of the cleaning devices to the free end of the spacer has almost half the edge length of the sieve frame.
The preferred embodiments will be explained in detail by means of the following drawings.